1. 1 Inferring Ground-level Nitrogen Dioxide Concentrations from OMI 14.12.2007 Martin Steinbacher, Empa Edward Celarier, SGT Inc. Eric Bucsela, NASA GSFC Edward Dunlea, CIRES Joseph Pinto, U.S. EPA Lok Lamsal, Randall Martin, Aaron van Donkelaar AGU Fall Meeting, 10-14 Dec 2007, San Francisco, CA

2. 2 Large regions lack sufficient in-situ data for air quality NO 2 associated with mortality Limitations of current NO 2 networks  Insufficient NO 2 measurements for air quality  NO 2 measurements contaminated by reactive nitrogen species Satellite-derived surface NO 2 complement the existing ground-based networks NO 2 monitoring networks

3. 3 Tropospheric column as a proxy for surface NO 2 No profile information in satellite measurements 70-90% of tropospheric column in polluted boundary layer San Francisco Los Angeles Phoenix Houston Dallas Chicago Toronto OMI tropospheric NO 2 column (standard product)

4. 4 Approach to derive surface NO 2 from OMI S  Surface NO 2   Tropospheric NO 2 column Information of NO 2 profile shape from GEOS-Chem GEOS-CHEM In situ Texas AQS (Martin et al, 2004) GEOS-Chem (2x2.5 o ) OMI (2x2.5 o ) OMI (0.2x0.2 o ) GG OO  F  free tropospheric NO 2

5. 5 OMI-derived surface NO 2 over North America ppb Seasonal average (SON) Seasonal mean <0.1 ppbv in rural areas >10 ppbv in urban areas

6. 6 Validation data sources for OMI-derived surface NO 2 DOAS, LIF, TILDAS Chemiluminescent NO x analyzer Molybdenum converter Photolytic converter Research grade instruments Photochemical steady state NO 2 (PSS-NO 2 ) Typical air quality monitor J NO2 from Fast-J radiative transfer model (Cloud filtered)

7. 7 Interference in molybdenum converter measurements See Dunlea et al, 2007; Steinbacher et al., 2007 for interference CompoundsConversion efficiencyExperiments NO 2, ethyl nitrate ~ 100% Winer et al., 1974 PAN92%Winer et al., 1974 HNO 3, PAN, n-propyl nitrate, n-butyl nitrate ≥98%Grosjean and Harrison, 1985 Inlet loss of HNO 3 35% for HNO 3 inferred comparing with photolytic converter

8. 8 Corrected molybdenum best reproduces photolytic NO 2 Taenikon, Switzerland Photolytic Molybdenum  (>60%, R 2 =0.96) Molybdenum cor.  (< 4%, R 2 =0.95) PSS-NO 2  (6-20%, R 2 =0.86)

9. 9 Correlation between in-situ and OMI-derived surface NO 2 296 stations Correlation 0.3 to 0.85 Stronger correlation in polluted areas 53 stations Stations with PSS-NO 2 > molybdenum not selected OMI versus corrected in-situ OMI versus PSS-NO 2

10. 10 General overall agreement DJF MAM JJA SON OMI Cor. in-situ PSS- NO 2

11. 11 Comparison between in-situ and OMI-derived surface NO 2 corrected in-situ OMI-derivedPSS-NO 2 uncorrected in-situ

12. 12 Comparison between OMI and in-situ measurements according to land use type OMI-derived surface NO 2 is biased low by 6 to 40% Seasonal bias in OMI-derived surface NO 2

13. 13 Conclusions Promising approach for inferring ground-level NO 2 from satellite Surface measurements provide indirect validation of OMI tropospheric NO 2 column Acknowledgement This work is supported by NSERC and NASA

14. 14

15. 15 Approach to derive surface NO 2 from OMI GEOS-Chem (2x2.5 o ) OMI (2x2.5 o ) OMI (0.2x0.2 o ) Dallas, TX GG OO S → Surface NO 2  → Tropospheric NO 2 column  F → free tropospheric NO 2 column SOSO

16. 16 Approach to derive surface NO 2 from OMI  F → free tropospheric NO 2 column ( a ) ( b ) percent difference (b – a)

17. 17 Interference in molybdenum converter measurements Molybdenum Conv. DOAS OMI GOME-2 SCIA GOME Results from Mexico City Metropolitan Area (MCMA) field campaign, 2003

18. 18 Interference for US and Canadian sites during OMI overpass time Larger interference in summer Larger interference in clean areas Interference during OMI overpass time can be up to a factor of 3 over land CF=